More than 3 million southerners have signed up for the 9 January poll, which is likely result in Africa's largest country being split in two. Disputes and delays in registering voters had led many to suggest that the vote for an independent south Sudan would have to be postponed – a dangerous outcome, given the huge weight of expectation there.

However, aided by a renewed international engagement over the past two months, the registration process has passed peacefully and smoothly in the semi-autonomous south.

Despite the registration window being extended for a week until today, hopes are high that the vote will still go ahead on schedule.

"Logistical challenges remain but things look to be on track," said John Ashworth, an analyst who works with Sudan's churches. "The momentum is there, and 99% of the international community now say it should happen on time."

South Sudan's right to choose secession stems from the 2005 comprehensive peace agreement, which ended a 20-year civil war between the non-Arab south and the Arab-led north that claimed more than 2 million lives.

The referendum is open to all southerners, including those living in northern Sudan and the diaspora. A separate and simultaneous referendum will take place in Abyei, an oil-producing area on the north-south border.

Though the peace has held for the past six years, the mistrust between the ruling Sudan People's Liberation Movement (SPLM) in the south and the president Omar al-Bashir's National Congress party (NCP) in the north has not disappeared.

About three-quarters of Sudan's 500,000 daily barrels of oil come from the south, and while this revenue is currently shared between the two sides, the north will lose out if the country splits. Many southerners believe Bashir will try to postpone their bid for freedom to avoid giving up much of the country's petrodollar income.

These suspicions led to many of the southerners living outside south Sudan refusing to register for the referendum, fearing that the Khartoum government will tamper with their votes.

The April elections that saw Bashir returned to power for another term were plagued with irregularities in the north and, to a lesser extent, in the south. For its part, the SPLM, which is mindful of the situation in western Sahara, where Morocco has blocked an internationally agreed referendum on independence for Saharawis since 1991, warned at the weekend it would not accept a delay in the poll "even for a single day".

While the UN and international community will have to play a prominent role in ensuring there is no delay – printing of ballot papers has not yet begun and the African Union last week described the referendum schedule as "desperately tight" – diplomats are also concentrating on persuading the NCP not to sabotage the process.

The US has been leading the effort, offering Bashir and his government incentives, from an easing of sanctions to debt relief, as long as the vote is free and fair and the outcome respected.

But understanding the true intentions of northern leaders is difficult, and nobody outside Khartoum knows how the politicians will react if the vote comes out in favour of secession.

"The NCP does not have a collective will on this and I don't think it even knows [what] it will do," said John Ryle, chairman of the Rift Valley Institute, a research and advocacy organisation that issued a recent report on the referendum. "Northern Sudanese in general have not yet woken up to what separation might mean." Adding to the uncertainly over the post-referendum situation is the failure to implement key parts of the comprehensive peace agreement, including the demarcation of the north-south border.

The SPLM and NCP have also not agreed on how the oil would be managed in future, which is critical since the only pipelines from the southern oilfields run through the north.

Zach Vertin, Sudan analyst at the International Crisis Group thinktank, who wrote a recent report on the country's future, said Bashir's government was stalling to extract as many concessions from the south and the international community as possible.

But he added that "the chances of a delayed vote have diminished in recent weeks".

The Abyei referendum, which will see residents vote on whether to join the north or south, remains in doubt however, and Vertin said there may have be a negotiated settlement – "Abyei to the south in return for X" – instead of a vote.

Regardless of what the NCP can negotiate, a divided Sudan will weaken its hand in the north.

Opposition politicians are likely to blame Bashir for the country breaking up, and the loss of a large chunk of oil revenue will also hurt.

This uncertainty has led to some Sudan-watchers to suggest that Bashir would consider using force to prevent secession.

But Vertin disagrees: "The prospect of a return to large-scale conflict is limited. There's lots of positioning and rhetoric but neither side wants war, or has anything to gain from it. It would be a lose-lose scenario."